1. Field of the Invention
The present invention relates to attractant lures for trapping flying insects, such as mosquitoes, no-see-ums, and other insects that are attracted to components of sweat and breath emanating from mammals, and systems related thereto.
2. Description of Related Art
Each year mosquito-transmitted diseases are responsible for over 3 million deaths and 300 million clinical cases. It is estimated that the worldwide costs associated with the treatments of mosquito-transmitted diseases run well into the billions of dollars. In many regions mosquitoes are the primary transmitters of debilitating diseases such as malaria, yellow fever, dengue fever, encephalitis, West Nile virus, sleeping sickness, filariasis, typhus and plague. In addition to the illnesses and deaths caused to humans, mosquito-transmitted diseases are a major cause of economic losses to livestock industries due to veterinary diseases. Further, mosquito-transmitted diseases pose an ever-present concern to regions dependent on revenues from tourism. Specifically, the presence of such diseases in a given region is believed to relate to the willingness of tourists to select that region as a tourism destination.
With increased travel and world commerce it also is expected that some of these insect-borne diseases will become major health problems in the continental United States and elsewhere. For example, the emergence of the West Nile virus in temperate regions of Europe and North America supports this expectation, which represents a threat to public, equine and animal health. Viral infection of host animals can result in encephalitis (inflammation of the brain) in humans and horses, and mortality in domestic animals and wild birds.
In 1995, endemic cases of malaria were recorded in California and New Jersey, and several cases of dengue fever were diagnosed in southern Texas. In September 1996, an unprecedented number of mosquitoes were found in Rhode Island carrying Eastern Equine Encephalitis. Test results revealed that one out of 100 mosquitoes trapped were carrying this rare, deadly virus that has a mortality rate of 30% to 60%. The situation in Rhode Island was so severe that the governor declared a state of emergency. In 1997, a similar situation occurred in Florida with an outbreak of St. Louis Encephalitis.
Dengue fever is a particularly dangerous mosquito-transmitted disease that is increasingly becoming a problem of global proportions and may soon eclipse malaria as the most significant mosquito-borne viral disease affecting humans. Dengue fever's global distribution is comparable to that of malaria, with an estimated 2.5 billion people living in areas at risk for epidemic transmission. Each year, millions of cases occur, and up to hundreds of thousands of cases of dengue hemorrhagic fever (DHF) are diagnosed. The case-fatality rate of DHF in most countries is about 5%, with most fatal cases occurring among children.
Until recently, dengue fever was relatively unknown in the Western Hemisphere. In the 1970s, a dengue epidemic swept through Cuba and other parts of the Caribbean. In 1981, a second serotype, which was accompanied by hemorrhagic fever, broke out in Cuba. That second epidemic resulted in more than 300,000 hemorrhagic fever cases, and more than 1,000 deaths, most of which were children. By 1986, other countries in South America and Mexico began to see a significant rise in dengue fever. The summer of 1998 saw a new outbreak on the island of Barbados.
With respect to the mainland Americas, nearly 24,000 cases of dengue fever were reported during the first eight months of 1995 in Central America, including 352 cases of hemorrhagic fever. El Salvador declared a national emergency due to the widespread infestation of this disease in that country in 1995. Even Mexico recorded approximately 2,000 cases in 1995, 34 of which included hemorrhagic fever. In total, the Pan American Health Organization reported that there have been almost 200,000 cases of dengue and more than 5,500 cases of hemorrhagic dengue fever in the Americas.
Entomologists are very concerned about the increased threat of dengue fever to the United States. This concern is attributable in part to the presence of the recently arrived species of mosquito known as the Aedes albopictus. A. albopictus (also called the “tiger mosquito” due to its bright striping and aggressive biting) was first discovered in the United States in 1985 in Harris County, Texas, the county in which the city of Houston is sited. Historically, the tiger mosquito has been a major transmitter of dengue fever in Asia. It is believed that the introduction of the tiger mosquito in the United States can be traced to a shipment of old tires from Japan. In 1991, the Eastern Equine Encephalitis virus was discovered in groups of tiger mosquitoes found in a tire pile just 12 miles west of Walt Disney World in Orlando, Fla. As of February 1996, established populations of the tiger mosquito have been documented in 24 states.
Most alarming is that the tiger mosquito has now demonstrated the ability to survive in states as far north as Ohio, New Jersey, and Nebraska. Unlike the yellow fever-carrying mosquito Aedes aegypti, the tiger mosquito's eggs can survive very cold winters. As a result, the tiger mosquito has great potential to carry diseases into a substantial portion of the United States. The tiger mosquito is already proving a nuisance and hazard in Pulaski County, Illinois, where bite counts of the insect were 25 per minute. In central United States, this species has been linked to the transmission of La Crosse Encephalitis, an often fatal disease.
Hamatophagous flying insects, such as mosquitoes, are attracted to kairomones, which are generally metabolic byproducts released by mammalian systems. During anaerobic metabolic reactions, such as intense muscle activity, pyruvate is reduced by NADH to form lactate. Such activity also produces sweat, which in its most basic form, is an aqueous solution lactic acid, urea and ammonia. Lactic acid, cutaneously excreted from mammalian organisms in sweat and exhaled in breath, has been found to be a mild, close-range kairomone, particularly for A. aegypti. However, when combined with carbon dioxide (CO2), a long-range kairomone for many hematophagous insects, lactic acid produces a synergistic effect, greatly enhancing the attraction of mosquitoes thereto (see, for example, Smith et al., Annals Ent. Soc. Am. 63(3), 760–770, 1970, the contents of which are incorporated by reference in their entirety).
The ability of flying insects to track hosts by scent is mediated by chemoreceptors in their antennae. Sensilla basiconica of varying length are positioned on the antennae for discriminate sensing of, for example, lactic acid (short sensilla basiconica), CO2 (long sensilla basiconica) and butyric acid (short and long sensilla basiconica). The attraction of flying insects to lactic acid is concentration-dependent, with no detectable attraction at low concentrations, and actually repelling flying insects at high concentrations. At concentrations typically found on human skin, lactic acid demonstrates true attractiveness for A. aegypti, and does not function as a repellant. Thus insects use metabolic byproducts released from mammalian hosts, such as lactic acid, in locating targets for potential meals.
The odors emanating from differing species vary in attractiveness to flying insects, and may be influenced by the chemical composition of individual scent. Thus, compounds comprising human odor may be more attractive to flying insects than the odor released by cats or cattle, establishing a hierarchy of preferential hosts sought by such insects. Individual preferences of flying insects for specific hosts may also be influenced by body temperature, moisture content in secretions, and even visual cues. The compound 1-octen-3-ol, heavily produced by bovines and is known to entice mosquitoes to their ruminant sources. The addition of lactic acid to odor samples from non-human animals, including samples containing 1-octen-3-ol, appears to increase mosquito attraction. Thus, evidence indicates that lactic acid is a primary factor involved in flying insect chemo-attraction.
A number of methods for controlling mosquito populations or repelling mosquitoes have been proposed in the past. Some examples of these are discussed below. As will be appreciated from the following discussion, each of these methods has significant drawbacks, rendering them impractical or ineffective.
One well-known method for suppressing mosquito populations is the use of chemical pesticides, such as DDT and malathion. In general, two types of mosquito pesticides available—adulticides and larvicides. Adulticides are chemicals used to kill mosquitoes that have developed to the adult stage. Infested areas are primarily sprayed from aircraft or motor vehicles. Efficacy of the sprayed chemicals is typically dependent upon wind, temperature, humidity, time of day, the particular mosquito's resistance to the chemical used, and the base efficacy of the particular chemical. Adulticides must be applied for each generation of adults produced by rain, tidal flooding, or other periodic egg hatching trigger, and have a typical efficacy window of only a half-day. As such, these chemicals must be applied at a time when maximum contact with adult mosquitoes can be expected.
Larvicides, on the other hand, are applied to water sources to kill the larvae before they become adult mosquitoes. Larvicides generally take the form of one of three varieties: (1) an oil applied to the water surface that prevents the larvae from breathing and thus drowns them, (2) a bacteria like BTI (Bacillus thuringiensis israelensis) which attacks the larvae and kills them, or (3) a chemical insect growth regulator (e.g., methoprene) that prevents the larvae from developing to the adult stage. Unfortunately, larvicides are often not particularly effective for a variety of reasons. For one, most larvicides have a short efficacy period and must be applied to the water while the immature mosquitoes are at a particular stage of growth. Several species of mosquitoes, such as tree-hole breeders, root-swamp breeders, and cattail-marsh breeders, are not easily controlled with larvicides, since the larvae either do not come to the surface (e.g., cattail marsh mosquito) or the water sources are so difficult to locate that the larvicides cannot be economically applied (e.g., tree holes).
For another, the mosquito that carries the West Nile virus (Culex pipiens) lives and breeds around humans in gutters, underground drains, flower pots, birdbaths, etc. This makes the spraying of larvicides impractical due to the difficulty associated with effectively targeting such areas. In addition, many people are uncomfortable with the use of chemicals so close to their homes.
Regardless of their efficacy, or lack thereof, the use of chemical pesticides has reduced dramatically in both the United States and worldwide. A primary reason for this reduction is the rising public awareness of the potential health hazards related to pesticide use. Specifically, general public perception of the long-term health and environmental hazards presented by certain chemicals (e.g., DDT) has led to the banning of their use for mosquito control in many parts of the United States and other countries. Additionally, increasing pesticide resistance among mosquitoes has reduced the effectiveness of conventional chemical control means, thus bolstering an argument that the benefits of pesticides are outweighed by public health risks.
To some extent, natural predators also control mosquito populations. For example, certain fish and dragonflies (as both nymphs and adults) are reported to be predacious to mosquito larvae and adults. Additionally, it is known that certain bats and birds also prey on mosquitoes. It has been advocated by some people, particularly those opposed to the use of pesticides, that natural predators should be relied on as an environmentally safe means of controlling mosquito populations. Unfortunately, efforts in the past to utilize natural predators for effectively controlling mosquito populations have proven ineffective. For example, large bat towers were erected in three cities in the South during the 1920s with high expectations that the bats living in these towers would control mosquito populations. However, these towers were ineffective at adequately controlling the local mosquito populations. Studies of the stomach contents of the bats found that mosquitoes made up less than 1% of their food source.
Many people rely on repellents to keep mosquitoes away from their person, or from a certain area. These repellents by their nature do nothing to actually control the mosquito population; instead, they simply offer temporary relief to the person employing the repellent. Repellents can be either topical or aerial, and can take many forms, including lotions, sprays, oils (e.g., “Skin-So-Soft”), coils, and candles (e.g., citronella), among others. The most common repellents (lotions, sprays, and oils) are those that are used on the clothing or body. Many of these repellents do not actually “repel” mosquitoes per se. Rather, some repellents simply mask the factors (CO2, moisture, warmth and lactic acid), which attract a mosquito to its host. Although these repellents are fairly inexpensive, they often have an offensive odor, are greasy, and are effective for only a limited duration. It has also been found that repellents, which contain DEET (N, N, diethyl-m-toluamide), or 2-ethyl-1,2-hexanediol, actually become attractive to mosquitoes after a period of time. Therefore, it is advisable when using repellents to wash them off or reapply fresh repellent when the protective period has passed.
In addition to being unpleasant, many repellents are coming under close scrutiny with respect to the potential long-term health hazards they may pose. DEET, considered by many entomologists to be the best repellent available, has been marketed for over 30 years, and is the primary ingredient of many well-known commercial sprays and lotions. Despite the long-term widespread use of DEET, the U.S. Environmental Protection Agency (EPA) believes that DEET may have the ability to cause cancers, birth defects, and reproductive problems. The EPA issued a consumer bulletin in August 1990 in which it stated that a small segment of the population may be sensitive to DEET. Repeated applications, particularly on small children, may sometimes cause headaches, mood changes, confusion, nausea, muscle spasms, convulsions or unconsciousness.
Mosquito coils have been sold for many years as a means for repelling mosquitoes. These coils are burnt to emit a repellent smoke. Products manufactured about 20 years ago such as Raid Mosquito Coils contained the chemical allethrin. Recent products such as OFF Yard & Patio Bug Barriers contain the chemical esbiothrin. Although these products may provide some relief from mosquito activity, they do not, however, reduce the number of mosquitoes in a region. In addition, they also emit smoke and chemicals into the vicinity. Moreover, with even the slightest breeze the smoke and chemicals are dispersed over a large area becoming diluted and less effective, thereby diminishing their potential effects.
Many people have also touted the benefits of citronella in repelling mosquitoes, whether it is in the form of candles, plants, incense, or other mechanisms. According to a recent study, citronella-based products have been shown to be only mildly effective in repelling mosquitoes and then only when the candles were placed every three feet around a protected area. This treatment was only slightly more effective than burning plain candles around a protected area. In fact, it is believed that burning the candles increases the amount of CO2 in the air, causing more mosquitoes to be drawn into the general area rather than reducing the number of mosquitoes in the area. Despite these drawbacks, the current market for citronella-based products is quite large.
Introduced in the late 1970s, the familiar “black-light” electrocution devices, commonly referred to as “bug zappers,” were initially a commercial success. Although totally ineffective at killing mosquitoes, bug zappers sell at a current rate of over 2 million units annually. The inability of these devices to kill mosquitoes has been proven in academic studies and from the personal experiences of many bug zapper owners. Specifically, electrocution devices do not kill mosquitoes because they do not attract mosquitoes. These devices only attract insects that are attracted to light, which is not the case with mosquitoes.
Wigton et al. (U.S. Pat. No. 6,145,243, the contents of which are incorporated in their entirety herein by reference) disclose an insect trapping device developed by the American Biophysics Corporation of East Greenwich, R.I. Wigton et al. disclose the basic construction of a device that generates a flow of CO2 for attracting mosquitoes and other flying inspects towards an inlet on the device. A vacuum draws the insects attracted by the CO2 through the inlet and into a trap chamber. The trap chamber includes a disposable mesh bag in which the mosquitoes become dehydrated. When the bag becomes full, it can be removed and replaced.
While the device disclosed in Wigton et al. has been commercially successful for American Biophysics Corporation, further product development efforts by the inventors of the present application have yielded a number of improvements that are directed to reduce the manufacturing costs and operational efficiency of the device of Wigton et al. As a result of these improvements, the efficacy of the device has increased, while the cost structure of the device of the present application can be reduced, thereby making the technology more widely available to the average consumer. It is believed that the additive impact of widespread use of this technology will help lead to better control of mosquito and other flying insect populations and, in turn, to reduced incidents of insect-transmitted diseases.
Other devices, such as the mosquito trap disclosed in Brittin et al. (U.S. Pat. No. 6,209,256, the contents of which are incorporated in their entirety herein by reference) employ a combination of CO2 and other lures to entice flying insects to their demise. Brittin et al. provide an entrapping media, which may be fortified with chemical lures. Flying insects are attracted to the device by the CO2 emanating from it. Upon entering the housing of the device, insects are blown by a fan into the entrapping media, where the insects drown. The entrapping media may contain, one or more attractants, such as lactic acid, to better entice insects to their demise. A similar device (The mosQUITo™ Eradicator), disclosed at http:www.allnaturessafeway.com (as of Apr. 30, 2002), employs combinations of lactic acid and octenol lures in the entrapping media. A major drawback of these devices is the entrapping media itself, which may leak or splash from its open entrapping tray, thereby exposing the user to the chemicals and insects contained therein. Moreover, the entrapping media tray must be cleaned periodically. In addition, insects trapped within this device are not suitable for live study.
By far, the most significant drawback of lures in the form disclosed by Brittin et al. is the inability to ensure a steady release of attractant over time. The open tray design of Brittin et al. provides a large surface area for the chemical lure to escape in an unregulated manner. Initially, large amounts of lure are released into the atmosphere, which drop off rapidly, particularly for highly volatile attractant compounds. Fresh lure liquid may be needed in a matter of days to provide a level of attractant sufficient for enticing flying insects to the traps.
Therefore, there exists a need in the industry for a system that attracts flying insects, in which the attractant is relatively non-toxic to human beings and household pets, the attractant is produced at a steady, constant rate and has a long useful life.